1. Field of the Invention
The invention pertains generally to an interstage separator for transferring hot rubber crumb from a hot, wet first stage air stream to a cool, dry second stage air stream.
A typical dewatering and drying process for rubber crumb involves utilizing an extruder discharging to a pneumatic conveying system. The rubber particles are cooled in the conveying system, and are thence conveyed to and discharged onto an enclosed vibrating conveyor or fluidized bed conveyor. The rubber particles are further cooled down to baling or packaging temperature requirements in the vibrating conveyor or fluidized bed conveyor, being subsequently transported via a series of open vibrating conveyors to a baling or packaging area.
The level to which the rubber crumb is able to be cooled in the pneumatic conveying system is limited by the saturation temperature of the air and steam mixture in the pneumatic conveying system. Lowering of the air temperature below the saturation temperature of the wet hot air in the pneumatic conveying system in an effort to obtain additional cooling of the rubber crumb results in the product being undesirably wetted by the free water which is formed. Hence, it is necessary to direct the rubber crumb to the enclosed vibrating or fluidized bed conveyor for further cooling as previously noted.
The cooling limitations imposed in existing pneumatic conveyor systems, together with the peculiar properties of the rubber crumb, give rise to problematic deficiencies culminating in system performance and quality concerns. Because the rubber particles entering the enclosed vibrating conveyor or fluidized bed conveyor from the pneumatic conveyor are still hot, the particles agglomerate, thereby causing fouling of the equipment downstream of the pneumatic conveyor. Additionally, the hot rubber which causes the fouling tends to degrade and break away, resulting in contamination of the product. Moreover, the rubber agglomerations cause weight-control irregularities in the baling or packaging area.
Thus, the need exists for a process which allows cooling of the dried rubber crumb in an elastomeric polymer drying and cooling system to temperatures lower than those presently achievable with conventional systems, prior to presentation of the rubber crumb to conveying, baling or packaging stations. Applicant's co-pending patent application, filed simultaneously herewith, provides a process which realizes the latter objective by providing a method wherein rubber crumb is transferred from the water-saturated hot air stream of a first pneumatic conveyor, to a cool, dry air stream in a second pneumatic conveyor. Once the rubber particles are introduced into the cool dry air in the second pneumatic conveyor, the particles are subject to additional cooling over that which is able to be obtained in the first pneumatic conveyor. Indeed, the rubber particles may be cooled in the second pneumatic conveyor to such an extent that the enclosed vibrating conveyor or fluidized bed conveyor may be entirely eliminated.
The invention of the present application is directed to an interstage separator for transferring hot rubber crumb from a first stage pneumatic conveyor containing a hot, wet first stage air stream, to a second stage pneumatic conveyor containing a cool, dry second stage air stream. The invention accomplishes the preceding objective while avoiding agglomeration of and sticking of the rubber crumb in the interstage separator.
2. Description of the Prior Art
It is known in the prior art to separate particles from an air stream. For example, U.S. Pat. No. 4,599,016, issued on July 8, 1986 to Medemblik, is directed to a cyclone apparatus for separating granular matter from an air stream.
It is also known in the prior art to cause a product to be contacted by a counterflowing reaction or cooling gas. Exemplary of this teaching is U.S. Pat. No. 4,441,261, issued on Apr. 10, 1984 to Beckmann. Beckmann discloses a cooling apparatus to which red-hot coke is introduced and wherein two cooling gas streams combine with each other at the upper end of the apparatus. The cooling gas streams are supplied to the apparatus through gas distributors proximate its lower end and are directed in a direction opposite to that of the flowing coke material.
Similarly, U.S. Pat. No. 4,365,057, which issued to Saito et al on Dec. 21, 1982, teaches a drying machine to which nitrogen gas is supplied at the lower part thereof, and ascends in the machine in counterflow to a descending hydrocarbon medium.
U.S. Pat. No. 4,231,991, issued to Mueller on Nov. 4, 1980, shows a crystallization apparatus to which is admitted a granular amorphous material. The material descends by gravity in counterflow to a hot gas admitted to the lower portion of the apparatus.
U.S. Pat. No. 4,189,299, issued on Feb. 19, 1980 to Bourne, discloses a cooling tower for receiving hot lime. Cool air is drawn into the cooling tower near its bottom, flows up through the falling lime and is pulled into dust deparators near the top of the tower.
Gardner, U.S. Pat. No. 4,076,493 dated Feb. 28, 1978, shows an upright shell which is adapted to contain sintered particulate material to be cooled, and air distributing means arranged within the lower portion of the shell for releasing cooling air into the material.
U.S. Pat. No. 3,629,951, issued to Davis et al on Dec. 28, 1971, is directed to a spray tower wherein a hot air duct passing to a plenum is provided at the lower end of the tower for distributing hot air into the tower.
U.S. Pat. No. 3,265,775, issued on Aug. 9, 1966 to Friedrich, discloses a stand pipe and funnel apparatus having a lower inlet conduit for admission of treatment gas for upward flow into the stand pipe.
A contact gas reaction means is shown in U.S. Pat. No. 2,458,357, which issued on Feb. 19, 1944 to Evans. Evans illustrates a regeneration vessel confining a contact material, and to which cold air is provided for both upward and downward flow within the vessel.
Finally, U.S. Pat. No. 2,436,355, issued on Feb. 17, 1948 to Cadot et al is directed to a spray-drying chamber into which hot air is drawn. Additionally, auxiliary cold air is forced into the chamber through annular rings at the top and bottom.
The prior art fails to teach or suggest an interstage separator particularly adapted to transfer hot rubber crumb from a hot wet first stage air stream to a cool dry second stage air stream without fouling of the associated equipment, and contamination or degradation of the product, and which minimizes entrained first stage vapor in the second stage stream. Additionally, the prior art reflects a series of counter current flow devices. The present invention, on the other hand, is representative of co-current flow relative to the second stage air stream and solids.